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1B Neurology & Neuroscience > Auditory system > Flashcards

Auditory system Flashcards

1
Q

what is the anatomy of the auditory system?

A
  • Divided into 3 sections
    • Outer, middle and inner ear
  • Each part has specific function
  • Organ embedded in petrous portion of temporal bone (hardest bone in body)
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2
Q

what is the function of the outer ear?

A

capture sound and focus it on the tympanic membrane

amplify some frequencies by resonance in the canal

protect the ear from external threats

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3
Q

what is the function of the middle ear?

A
  • Main function is amplification by:
    • Focusing vibration from large surface area (tympanic membrane) to smaller surface area (oval window)
      • Change surface area means pressure in increased
    • Using leverage from incusstapes joint to increase force on oval window
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4
Q

what is the function of the inner ear?

A
  • Hearing part inner ear is cochlea
  • Function = transduce vibration into nervous impulses
  • While doing so produces a frequency (pitch) and intensity (loudness) analysis of sound
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5
Q

what does the cochlea contain?

A

3 compartments

  • Scala vestibuli
  • Scala tympani
  • Scala media
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6
Q

what are the scale vestibuli and tympani?

A

bone structures

contain perilymph (high in sodium)

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7
Q

what is the structure of the scala media?

A

membranous structure

contains endolymph (high potassium)

hearing organ of Corti location

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8
Q

what is the structure where the organ of corti lies?

A

basilar membrane

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9
Q

how is the basilar membrane arranged?

A

tonotopically

sensitive to different frequencies at different points along length

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10
Q

what is the hearing organ?

A

organ of corti

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11
Q

what does the organ of corti contain?

A
  • Contains hair cells: inner (IHC) and outer (OHC)
  • IHC arranged on one column and OCH on three
  • tectorial membrane above hair cells
    • allow hair deflection, which will depolarise the cell
    • only OHC in constant contact with membrane
      • assists contacts with the IHC
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12
Q

what are the function of inner hair cells?

A

carry 95% afferent information of auditory nerve

function= transduction of sound into nerve impulses

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13
Q

what are the function of outer hair cells?

A

carry 95% efferent information of auditory nerve

function= modulation of sensitivity of response

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14
Q

what is the difference between inner and outer hair cells?

A

IHC arranged in one column, OHC on 3

OHC in constant contact with tectorial membrane

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15
Q

what are sterocilia?

A

hairs of hair cells

responsible for transduction

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16
Q

how does deflection of stereocilia work?

A

open K+ channels= deflection of sterocilia towards longest cilium

  • ionic interchange depolarises the cell= NT liberated
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17
Q

what are the effects of depolarisation in hair cells?

A

K+ channel opening

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18
Q

what happens to deflection of stereocilia with higher amplitude of sound?

A

higher amplitude of sound= greater deflection of stereocilia & K+ channel opening

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19
Q

what happens to stereocilia on hyperpolarisation?

A

closes K+ channels so noises arent as loud

20
Q

what is the pathway from the cochlear to cerebral hemisphere?

A
  • spiral ganglions from each cochlear project via auditory vestibular nerve (VIII) to ipsilateral cochlear nuclei
  • auditory information crosses at superior olive level
  • after this point all connections are bilateral
21
Q

how is hearing organised centrally?

A

tonotopically organised

22
Q

what is frequence / pitch?

A

(Hz)= cycles per second, perceived tone

23
Q

what is amplitude/loudness?

A

(db)

sound pressure, subjective attribute correlated with physical strength

24
Q

what is the human range of hearing?

A
  • freq = 20-20,000 Hz
  • loudness= 0dB- 120 dB sound pressure level (SPL)
25
Q

what is hearing acuity affected by?

A

decreases with age, particularly higher frequencies

26
Q

what are the types of hearing assessments?

A

tuning forks

audiometry

central processing assessment

tympanometry

otoacoustic emission

auditory evoked potentials

27
Q

what do tuning forks do?

A
  • establish probable presence or absence of hearing loss with significant conductive component
  • provide early and general information when audiometry is not available or possible
  • webber and rinne test
    • vibrate fork and see if hearing loss asymmetric or symmetric
    • not very specific tests
28
Q

what is audiometry?

A
  • science of measuring hearing acuity for variations in sound intensity and frequency
  • produce an audiogram where hearing thresholds plotted
29
Q

what is central processing assessment?

A
  • assessment hearing abilities via verbal and non verbal tests
    • e.g sound localisation, speech in noise, filtered speech
30
Q

what is tympanometry?

A
  • test middle ear and mobility of eardrum and conduction bones by creating vibrations of air pressure in ear canal
31
Q

what is otoacoustic emission?

A
  • low intestity sounds produced by normal cochlea
  • produced specifically by outer hair cells as expand and contract
  • part of newborn hearing screening and hearing loss monitoring
  • require no cooperation of subject
32
Q

what are the types of auditory evoked potentials?

A
  • electrocochleography
    • electrical activity from cochlea and 8th nerve- evoked by clocks or tone burst
  • auditory brainstem response (ABR)
    • electrical activity from 8th nerve and brainstem nuclei and tracts- evoked by clicks
  • late responses
    • electrical activity from primary auditory and association cortex- evoked by tone burst and oddball paradigm
33
Q

what are auditory brain stem responses and how are they used?

A
  • electrical responses from auditory pathway
  • ABR more commonly used in clinics
  • Does not require attention from patients
  • Alterations in latency of waves can point the location of deficit
34
Q

when might cortical potential be affected?

A

neurological condition or processing problems

35
Q

what are the types of hearing loss?

A

conductive hearing loss

sensorineural hearing loss

mixed hearing loss

36
Q

what is conductive hearing loss due to?

A

problem located in outer or middle ear

37
Q

what is sensorineural hearing loss due to?

A

problem located in the inner ear or auditory nerve

38
Q

what is mixed hearing loss due to?

A

conduction and transduction affected

problem affects more than one part of ear

39
Q

what are the degrees of hearing loss?

A

depends on where hearing thresholds are located

can be mild, moderate, severe or profound

40
Q

what are the causes of conductive hearing loss?

A
41
Q

what are the causes of sensorineural hearing loss?

A
42
Q

what are the treatments for hearing loss?

A
  1. Underlying cause
  2. Hearing aids/ cochlear implants/ brainstem implants
43
Q

what do hearing aids do?

A
  • Amplify sound, does not replicate any structure
44
Q

what do cochlear implants do?

A
  • Replaces function of hair cells by receiving sound, analysing and transforming into electrical signals
  • Send electrical impulse directly to auditory nerve
  • Required functional auditory nerve to function
45
Q

what do brainstem implants do for hearing loss?

A

Electrical signal sent to electrode in brainstem when auditory nerve affected- risky! Only bilateral nerve damage

1B Neurology & Neuroscience (14 decks)

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